Sunday, March 21, 2010

3/28/2010: More on Vaccines

Vet Tip of the Day: Vaccinating old horses
Key Words:  geriatric, immune system
A client called this week asking about recommendations for vaccinating old horses and mules.  She was wondering if her old retirees still needed all the same vaccinations that her younger, active, travelling horses receive.  I thought I would answer her question with a blog post so you could all share this information.  Please first review the two previous blog entries on vaccinations posted earlier this spring.  To find them you can type  - vaccination - into the search bar at the top of the blog home page  OR click on - vaccination - in the label group in the top left margin on the blog home page.
Let me reiterate that the decision to vaccinate any horse should be made based on an assessment of risk of disease to that horse and to the other horses in that horse's population group.  With this in mind, let's look at the geriatric horse in particular.  Your old horse's immune system is likely to look pretty much like your old horse does: it ages along with the rest of his body, inside and out.  When deciding whether or not to vaccinate the old fellow, consider the following: his body condition, his mobility, and his population dynamics.  Then think about each disease against with we vaccinate in the terms discussed in the previous blog posts.
Let's consider a contagious disease (spread from horse to horse) such as the upper respiratory viruses - Flu/Rhino.  Keep in mind that immunity to these viruses in general is relatively short lived in all horses.  Should your old horse contract influenza it may take longer for him to recover, and, under certain circumstances he may be at greater risk of developing complications such as pneumonia.  What are these circumstances? Living as part of a  large group of horses in a small area is probably the most threatening to an old horse.  If your horse has chronic lameness issues that cause him to spend significant periods of time lying down, again he is at increased risk of  secondary pneumonia.  If your horse is in poor body condition or has poor dentition, he is at greater risk of having difficulty shaking the flu.  If, however, your retired horse or horses are in good health, living in a large field without much contact with other horses, then their liklihood of contracting a contagious disease such as influenza or rhinopneumonitis is decreased, and should they "catch a cold", it is likely it will run its course without complication.  Under these conditions, you may choose not to vaccinate against Influenza or Rhinopneumonitis.

Concerning Strangles (Strep Equi)  the situation is somewhat different.  While Strangles is a highly contagious disease spread from horse to horse, it also is a disease which causes a powerful and long-lasting immune response in those exposed to the disease.  Because Strangles is common in our area of northern Nevada, most older horses have good naturally aquired immunity.  Therefore, Strangles is uncommon in older horses.  Unfortunately,  old, debilitated horses which do contract Strangles are definitely at higher risk of potentially life threatening complications.  I recommend Stranges vaccination in old horses only if they are living in a high risk environment such as a concentrated boarding barn with high turnover of population or on a breeding farm with high number of foals in close contact.

All older horses should be vaccinated against West Nile Virus.  The disease is sporadic and unrelated to population dynamics.  To contract West Nile Virus, an infected bird flies over your horse's location, a mosquito bites the bird and within a short period of time that same mosquite flies down and bites your old horse.  Old horses definitely are at greater risk of death should they contract West Nile Virus.

Tetanus?  Sleeping Sickness?  The killed vaccines used against these diseases are very effective and afford long lasting immunity.  If you have owned your old friend for years and know for sure that annual tetanus/encephalitis vaccine has been administered, I would be comfortable decreasing the frequency of that vaccination to every 3 years rather than annually.  If you select this route, BE SURE that your horse receives a tetanus toxoid (not tetanus antitoxin) should he develop a foot abscess or deep puncture wound.

Hopefully this information will be of use to you when deciding which vaccines are appropriate for your old horses.

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